Gas turbine swirl detection

ABSTRACT

A non-transitory computer readable medium with instructions stored thereon, the instructions executable by one or more processors for calculating base swirl in a gas turbine; and calculating relative swirl in the gas turbine. Also, a method for gas turbine maintenance, comprising identifying a combustor in need of repair or replacement within a gas turbine; and repairing or replacing the combustor; wherein said identifying comprises calculating base swirl of the gas turbine and calculating relative swirl of the gas turbine in order to associate a gas path from a thermocouple to the combustor in need of repair or replacement.

Power generating gas turbine systems may include a plurality ofcombustors located circumferentially upstream of the turbine. Thesecombustors may create an exhaust temperature pattern, which may beindicative of the health of the gas turbine system. This temperaturepattern can also identify individual combustors within the turbine whichmay be in need of repair or replacement, and knowledge of the swirl ofexhaust gases within the turbine aids in repair.

Swirl is the result of shifts in the exhaust pattern generated by agiven combustor downstream of another combustor. Some combustors mayemit relatively hot or cold streaks of gas when operating abnormally.Inordinately hot or cold streaks may be indicative of a problematiccombustor. In order to efficiently repair or replace a combustor, theidentification of the problematic combustor must occur. This may beaided by identification of the swirl pattern within the gas turbine.

The exhaust temperature from a gas turbine may be measured with acircumferential array of thermocouples positioned downstream from theturbine. These values provide information not only about the performanceof the turbine as a whole, but deviations from one sensor to the nextprovide information about “health problems” in a hot or cold section. Ifone combustor is running incorrectly or damaged, its exhaust may behotter or colder than average, resulting in a measurable temperaturedeviation in the exhaust. However, the flow rotates upon leaving thecombustor and going through the turbine, thereby generating swirl. Anapparatus and/or process which may identify the amount of swirl mayassist in identifying the azimuthal location of the measuredtemperature, such that it can be associated with the combustor itoriginated from. Conventionally, swirl information may only be availablefrom the gas turbine's manufacturer, and varies between engines and withengine operating conditions. Swirl information is used to identify whichcombustor is responsible for hot or cold exhaust paths, and is thereforeuseful for quick diagnosis and repair of faulty machines, and/or forhealth monitoring. This algorithm enables online identification of theswirl from gas turbine operational data, which is important if the swirlinformation is otherwise unavailable.

Access to swirl information may assist in relating measured temperaturedata back to a specific component of concern. Furthermore, the amount ofswirl may change as a gas turbine ages.

The present subject matter relates to a non-transitory computer readablemedium with instructions stored thereon, the instructions executable byone or more processors for: calculating base swirl in a gas turbine; andcalculating relative swirl in the gas turbine.

The present subject matter also relates to a method for gas turbinemaintenance, comprising: identifying a combustor in need of repair orreplacement within a gas turbine; and repairing or replacing thecombustor; wherein said identifying comprises calculating base swirl ofthe gas turbine and calculating relative swirl of the gas turbine inorder to associate a gas path from a thermocouple to the combustor inneed of repair or replacement.

The present subject matter provides swirl information by determining anup-to-date swirl number as a function of operating conditions, whichenables one to determine swirl from standard data which is availablefrom gas turbine systems and enables users to make health assessmentsfrom the data.

Embodiments of the subject matter are disclosed with reference to theaccompanying drawings and are for illustrative purposes only. Thesubject matter is not limited in its application to the details ofconstruction or the arrangement of the components illustrated in thedrawings. As used herein, “at least one” means one or more than one, and“and/or” means items listed may be included exclusively or incombination. Like reference numerals are used to indicate likecomponents, unless otherwise indicated.

FIG. 1 is a block diagram illustrating certain embodiments of thepresent subject matter.

The following embodiments of the present subject matter arecontemplated:

1. A non-transitory computer readable medium with instructions storedthereon, the instructions executable by one or more processors for:

calculating base swirl in a gas turbine; and

calculating relative swirl in the gas turbine.

2. The non-transitory computer readable medium of embodiment 1, whereincalculating base swirl comprises calculating (a) unsteady pressureamplitude as a function of angular position within the gas turbineand/or (b) mean-subtracted exhaust temperature as a function of angularposition within the gas turbine.3. The non-transitory computer readable medium of either embodiment 1 orembodiment 2, wherein calculating base swirl comprises calculating (a)unsteady pressure amplitude as a function of angular position within thegas turbine and (b) mean-subtracted exhaust temperature as a function ofangular position within the gas turbine.4. The non-transitory computer readable medium of any one of embodiments1 to 3, wherein calculating base swirl comprises determining the averageangular offset between the unsteady pressure amplitude as a function ofangular position within the gas turbine and mean-subtracted exhausttemperature as a function of angular position within the gas turbine.5. The non-transitory computer readable medium of embodiment 4, whereinthe average angular offset is a function of gas turbine load.6. The non-transitory computer readable medium of any one of embodiments1 to 5, wherein calculating base swirl comprises measuring pressureamplitude within the gas turbine and fitting the pressure amplitude tothe expression A*e{circumflex over ( )}(i*Θ_(d)), wherein A is aconstant coefficient, i is the square root of negative one, e is Euler'snumber, and Θ_(d) is the angular phase of the measured pressureamplitude.7. The non-transitory computer readable medium of any one of embodiments1 to 6, wherein calculating base swirl comprises measuringmean-subtracted gas path temperature within the gas turbine and fittingthe mean-subtracted gas path temperature to the expressionB*e{circumflex over ( )}(i*Θ_(t)), wherein B is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(t) isthe angular phase of the measured mean-subtracted gas path temperature.8. The non-transitory computer readable medium of embodiment 7, whereincalculating base swirl comprises measuring pressure amplitude within thegas turbine and fitting the pressure amplitude to the expressionA*e{circumflex over ( )}(i*Θ_(d)), wherein A is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(d) isthe angular phase of the measured pressure amplitude.9. The non-transitory computer readable medium of embodiment 8, whereincalculating base swirl comprises calculating a second swirl, whereinsaid second swirl is 2*π*(Θ_(t)−Θ_(d)).10. The non-transitory computer readable medium of embodiment 9, whereincalculating base swirl comprises determining the average angular offsetbetween the unsteady pressure amplitude as a function of angularposition within the gas turbine and mean-subtracted exhaust temperatureas a function of angular position within the gas turbine, and whereinthe average angular offset is cross correlated with the second swirl.11. The non-transitory computer readable medium of any one ofembodiments 1 to 10, wherein a reference database is updated in realtime with base swirl data as a function of gas turbine load.12. The non-transitory computer readable medium of any one ofembodiments 1 to 11, wherein calculating relative swirl comprisescalculating the difference between the base swirl and a reference swirl.13. The non-transitory computer readable medium of embodiment 12,wherein the reference swirl is retrieved from a reference database, andwherein the reference swirl is selected on the basis of turbine load.14. The non-transitory computer readable medium of either embodiment 12or embodiment 13, wherein the reference swirl comprises themean-subtracted exhaust temperature pattern for a plurality of samples.15. The non-transitory computer readable medium of any one ofembodiments 12 to 14, wherein the relative swirl is equal to across-correlation shift, wherein the cross-correlation shift is a phaseshift that gives the highest correlation coefficient between the baseswirl and reference swirl.16. A computer system comprising at least one processor coupled tomemory and the computer readable medium of any one of embodiments 1 to15.17. A gas turbine system comprising at least one gas turbine and thecomputer system of embodiment 16.18. The gas turbine system of embodiment 17, wherein the computer systemis configured to receive real time data input from at least onethermocouple.19. The gas turbine system of either embodiment 17 or embodiment 18,wherein the computer system is configured to receive real time datainput from at least one pressure sensor.20. A method for gas turbine maintenance, comprising:

identifying a combustor in need of repair or replacement within a gasturbine; and

repairing or replacing the combustor;

wherein said identifying comprises calculating base swirl of the gasturbine and calculating relative swirl of the gas turbine in order toassociate a gas path from a thermocouple to the combustor in need ofrepair or replacement.

21. The method of embodiment 20, wherein calculating base swirlcomprises calculating (a) unsteady pressure amplitude as a function ofangular position within the gas turbine and/or (b) mean-subtractedexhaust temperature as a function of angular position within the gasturbine.22. The method of either embodiment 20 or embodiment 21, whereincalculating base swirl comprises calculating (a) unsteady pressureamplitude as a function of angular position within the gas turbine and(b) mean-subtracted exhaust temperature as a function of angularposition within the gas turbine.23. The method of any one of embodiments 20 to 22, wherein calculatingbase swirl comprises determining the average angular offset between theunsteady pressure amplitude as a function of angular position within thegas turbine and mean-subtracted exhaust temperature as a function ofangular position within the gas turbine.24. The method of embodiment 23, wherein the average angular offset is afunction of gas turbine load.25. The method of any one of embodiments 20 to 24, wherein calculatingbase swirl comprises measuring pressure amplitude within the gas turbineand fitting the pressure amplitude to the expression A*e{circumflex over( )}(i*Θ_(d)), wherein A is a constant coefficient, i is the square rootof negative one, e is Euler's number, and Θ_(d) is the angular phase ofthe measured pressure amplitude.26. The method of any one of embodiments 20 to 25, wherein calculatingbase swirl comprises measuring mean-subtracted gas path temperaturewithin the gas turbine and fitting the mean-subtracted gas pathtemperature to the expression B*e{circumflex over ( )}(i*Θ_(t)), whereinB is a constant coefficient, i is the square root of negative one, e isEuler's number, and Θ_(t) is the angular phase of the measuredmean-subtracted gas path temperature.27. The method of embodiment 26, wherein calculating base swirlcomprises measuring pressure amplitude within the gas turbine andfitting the pressure amplitude to the expression A*e{circumflex over( )}(i*Θ_(d)), wherein A is a constant coefficient, i is the square rootof negative one, e is Euler's number, and Θ_(d) is the angular phase ofthe measured pressure amplitude.28. The method of embodiment 27, wherein calculating base swirlcomprises calculating a second swirl, wherein said second swirl is2*π*(Θ_(t)−Θ_(d)).29. The method of embodiment 28, wherein calculating base swirlcomprises determining the average angular offset between the unsteadypressure amplitude as a function of angular position within the gasturbine and mean-subtracted exhaust temperature as a function of angularposition within the gas turbine, and wherein the average angular offsetis cross correlated with the second swirl.30. The method of any one of embodiments 20 to 29, wherein a referencedatabase is updated in real time with base swirl data as a function ofgas turbine load.31. The method of any one of embodiments 20 to 30, wherein calculatingrelative swirl comprises calculating the difference between the baseswirl and a reference swirl.32. The method of embodiment 31, wherein the reference swirl isretrieved from a reference database, and wherein the reference swirl isselected on the basis of turbine load.33. The method of either embodiment 31 or embodiment 32, wherein thereference swirl comprises the mean-subtracted exhaust temperaturepattern for a plurality of samples.34. The method of any one of embodiments 31 to 33, wherein the relativeswirl is equal to a cross-correlation shift, wherein thecross-correlation shift is a phase shift that gives the highestcorrelation coefficient between the base swirl and reference swirl.

Provided is a non-transitory computer readable medium with instructionsstored thereon, the instructions executable by one or more processorsfor: calculating base swirl in a gas turbine; and calculating relativeswirl in the gas turbine.

According to certain embodiments, calculating base swirl comprisescalculating (a) unsteady pressure amplitude as a function of angularposition within the gas turbine and/or (b) mean-subtracted exhausttemperature as a function of angular position within the gas turbine.

Calculating unsteady pressure amplitude as a function of angularposition within the gas turbine and/or calculating mean-subtractedexhaust temperature as a function of angular position within the gasturbine may be done by azimuthal decomposition. Azimuthal decompositionis an acoustic and/or exhaust temperature approach wherein sine wavesare “fit” to a temperature pattern across angular position and/or anacoustics pattern across angular position. Any shift between the bestfit sine waves is the swirl as determined by azimuthal decomposition.Azimuthal decomposition calculates the cross-correlation between thecombustor unsteady pressure amplitude as a function of a predeterminedcan number within a combustor, the can number corresponding to a radialposition, and the mean-subtracted exhaust temperature as a function ofgas path radial position. With this data, the radial offset between cannumber and gas path number that maximizes a correlation coefficient isdetermined. This may be repeated for multiple data points as possible ina given power band. Next, for each power band, the method computes theaverage of the radial offsets that maximize the cross-correlationcoefficient. The result is an average radial offset between can number(which corresponds to an angular location) and gas path number (whichcorresponds to an angular location) as a function of load, this isdefined as the swirl. Azimuthal decomposition may be included in thecalculation of base swirl. The determination of base swirl may consistof azimuthal decomposition.

Calculating unsteady pressure amplitude as a function of angularposition within the gas turbine and/or calculating mean-subtractedexhaust temperature as a function of angular position within the gasturbine may be done by cross correlation. Cross correlation projects thecombustor pressure amplitude pattern onto the following expression:A*e{circumflex over ( )}(i*Θ_(d)), where A is a constant coefficient, iis the square root of −1, e is Euler's number (approximately 2.7183),and Θ_(d) is the angular phase of the pressure amplitude pattern.Similarly, the mean-subtracted gas path temperature pattern is projectedonto the function: B*e{circumflex over ( )}(i*Θ_(t)), where B is aconstant coefficient, i and e are number constants as described above,and Θ_(t) is the angular phase of the temperature pattern. This methodthen defines the swirl to be the phase difference between the pressureamplitude pattern and the gas path temperature pattern. In degrees, thisis equal to 2*π*(Θ_(t)−Θ_(d)). The shift with the highest correlation tothe observed temperature and pressure patterns represents the swirl.According to certain embodiments, this highest correlation to theobserved temperature and pressure patterns may be represented as asingle coefficient. Cross correlation may be included in the calculationof base swirl. The determination of base swirl may consist of crosscorrelation.

The determination of base swirl may consist of azimuthal decompositionand cross correlation. Azimuthal decomposition and cross correlation mayboth be included in the calculation of base swirl, and may be providedas a check on one another. In certain embodiments, both azimuthaldecomposition and cross correlation are included in the determination ofbase swirl, and the determination of swirl in each is compared with oneanother to ensure a high confidence base swirl. The determination ofbase swirl may consist of azimuthal decomposition, cross correlation,and comparing the azimuthal decomposition swirl and cross correlationswirl.

Calculating relative swirl within a gas turbine may include autocorrelation. The relative swirl is the difference between the swirl atany given operating condition and the known swirl (reference swirl) at areference condition. The reference swirl may be known from experiencewith the gas turbine. The reference swirl may be determined by manuallycomparing pressure dynamics data to gas path temperature data. First,the auto correlation may average the mean-subtracted exhaust temperaturepattern for many samples at the reference condition, thereby definingthe reference pattern. Next, auto correlation may average themean-subtracted gas path temperature pattern over many samples at theoperating condition of interest, thereby defining the test sample. Thus,auto correlation correlates the reference pattern with the test pattern.Finally, auto correlation determines that the relative swirl is equal tothe correlation shift that gives the highest correlation coefficient.The shift with the highest correlation to the observed temperature andpressure patterns represents the swirl. According to certainembodiments, this highest correlation to the observed temperature andpressure patterns may be represented as a single coefficient. Autocorrelation may be included in the determination of relative swirl. Thedetermination of relative swirl may consist of auto correlation.

In some embodiments, the temperature cross correlation may be evaluatedaccording to Equation 1:

$\begin{matrix}{{{Temperatures}\text{:}\mspace{14mu} {\rho\left( {\bullet \; c} \right)}} = \frac{\sum\limits_{1}^{N}{{\overset{\rightarrow}{T}(c)} \cdot {\overset{\rightarrow}{T}\left( {c - {\Delta \; c}} \right)}}}{\sum\limits_{1}^{N}{{\overset{\rightarrow}{T}(c)} \cdot {\overset{\rightarrow}{T}(c)}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

{right arrow over (T)} can be a vector of temperatures from each of thethermocouples, N can be the number of thermocouples, c can be the indexfor a given thermocouple, and Δc can be the index shift of which thecorrelation is a function. The thermocouple indices represented by c canrange from 1 to N and can be periodic.

In certain embodiments, the pressure cross correlation may be evaluatedaccording to Equation 2:

$\begin{matrix}{{{Pressures}\text{:}\mspace{14mu} {\rho\left( {\bullet \; c} \right)}} = \frac{\sum\limits_{1}^{N}{{\overset{\rightarrow}{p}(c)} \cdot {\overset{\rightarrow}{p}\left( {c - {\Delta \; c}} \right)}}}{\sum\limits_{1}^{N}{{\overset{\rightarrow}{p}(c)} \cdot {\overset{\rightarrow}{p}(c)}}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

{right arrow over (p)} can be a vector of pressures from each of thepressure probes, N can be the number of combustors, c can be the indexfor a given pressure probe, and Δc can be the index shift, of which thecorrelation is a function. The pressure indices represented by c canrange from 1 to N and can be periodic.

In certain embodiments, calculating base swirl comprises calculating (a)unsteady pressure amplitude as a function of angular position within thegas turbine and (b) mean-subtracted exhaust temperature as a function ofangular position within the gas turbine. According to some embodiments,calculating base swirl consists of calculating (a) unsteady pressureamplitude as a function of angular position within the gas turbine and(b) mean-subtracted exhaust temperature as a function of angularposition within the gas turbine.

Calculating base swirl may comprise determining the average angularoffset between the unsteady pressure amplitude as a function of angularposition within the gas turbine and mean-subtracted exhaust temperatureas a function of angular position within the gas turbine. In someembodiments, the average angular offset is a function of gas turbineload.

According to certain embodiments, calculating base swirl comprisesmeasuring pressure amplitude within the gas turbine and fitting thepressure amplitude to the expression A*e{circumflex over ( )}(i*Θ_(d)),wherein A is a constant coefficient, i is the square root of negativeone, e is Euler's number, and Θ_(d) is the angular phase of the measuredpressure amplitude. In some embodiments, the fitting may be performed bytaking a plurality of pressure measurements, given by N, which may beequal to the number of combustors within the gas turbine. p_(n)(θ) mayrepresent the N^(th) pressure amplitude as a function of angularposition θ. From these measurements, A and Â may be determined by theformulas:

$\hat{A} = {\frac{1}{N}{\sum\limits_{1}^{N}{{p_{N}(\theta)}e^{i\; \theta}}}}$A = Â θ_(d) = ∠ Â

In some embodiments, calculating base swirl comprises measuringmean-subtracted gas path temperature within the gas turbine and fittingthe mean-subtracted gas path temperature to the expressionB*e{circumflex over ( )}(i*Θ_(t)), wherein B is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(t) isthe angular phase of the measured mean-subtracted gas path temperature.In some embodiments, the fitting may be performed by taking a pluralityof temperature measurements, given by M, which may be equal to thenumber of combustors within the gas turbine. T_(M)(θ) may represent theM^(th) exhaust temperature measurement as a function of angular positionθ. From these measurements, B and {circumflex over (B)} may bedetermined by the following formulas:

$\overset{\hat{}}{B} = {\frac{1}{N}{\sum\limits_{1}^{N}{{T_{M}(\theta)}e^{i\; \theta}}}}$$B = {\overset{\hat{}}{B}}$$\theta_{t} = {\angle \overset{\hat{}}{B}}$

In some embodiments, calculating base swirl comprises: measuringpressure amplitude within the gas turbine and fitting the pressureamplitude to the expression A*e{circumflex over ( )}(i*Θ_(d)), wherein Ais a constant coefficient, i is the square root of negative one, e isEuler's number, and Θ_(d) is the angular phase of the measured pressureamplitude; and measuring mean-subtracted gas path temperature within thegas turbine and fitting the mean-subtracted gas path temperature to theexpression B*e{circumflex over ( )}(i*Θ_(t)), wherein B is a constantcoefficient, i is the square root of negative one, e is Euler's number,and Θ_(t) is the angular phase of the measured mean-subtracted gas pathtemperature. In some embodiments, calculating base swirl consists of:measuring pressure amplitude within the gas turbine and fitting thepressure amplitude to the expression A*e{circumflex over ( )}(i*Θ_(d)),wherein A is a constant coefficient, i is the square root of negativeone, e is Euler's number, and Θ_(d) is the angular phase of the measuredpressure amplitude; and measuring mean-subtracted gas path temperaturewithin the gas turbine and fitting the mean-subtracted gas pathtemperature to the expression B*e{circumflex over ( )}(i*Θ_(t)), whereinB is a constant coefficient, i is the square root of negative one, e isEuler's number, and Θ_(t) is the angular phase of the measuredmean-subtracted gas path temperature.

According to certain embodiments, calculating base swirl comprisescalculating a second swirl, wherein said second swirl is2*π*(Θ_(t)−Θ_(d)).

Calculating base swirl may comprise determining the average angularoffset between the unsteady pressure amplitude as a function of angularposition within the gas turbine and mean-subtracted exhaust temperatureas a function of angular position within the gas turbine, and whereinthe average angular offset is compared with the second swirl. An exampleof MATLAB® code which may be included on the non-transitory computerreadable medium for the sake of this comparison may be seen in Example1, which is provided only by way of example and not limitation.Initially, temperature and pressure amplitude patterns are determined atthe maximum load of the gas turbine. A variable may be assigned to themaximum load in megawatts, and as well as an array assigned to all ofthe data points at lower loads, wherein the load is measured as itsdifference from the maximum load. Then, data points are gathered for aplurality of temperature and pressure measurement devices at the loadswithin the array, and corresponded to the given load by taking thearithmetic average of the temperature and pressure measurements at givenloads. The difference between the temperature and pressure measurementsin terms of angular difference may be the swirl.

In some embodiments, the non-transitory computer readable medium maycomprise instructions for updating a reference database with base swirldata as a function of gas turbine load. According to certainembodiments, the reference database may be updated in real time. Thereference database may be included on the same non-transitory computerreadable medium or on a separate non-transitory computer readablemedium. In some embodiments, the base swirl may be calibrated only oncefrom the reference database. According to certain embodiments, thereference database is configured to be updated with new data as directedby the user.

Calculating relative swirl may comprise calculating the differencebetween the base swirl and a reference swirl. In some embodiments, thisreference swirl may be obtained from a database of known swirlscorresponding to a given gas turbine load. In some embodiments, thereference swirl is retrieved from a reference database, and wherein thereference swirl is selected on the basis of turbine load. According tocertain embodiments, the reference swirl comprises the mean-subtractedexhaust temperature pattern for a plurality of samples.

In certain embodiments, the relative swirl is equal to across-correlation shift, wherein the cross-correlation shift is a phaseshift that gives the highest correlation coefficient between the baseswirl and reference swirl. Provided by way of example and notlimitation, an example of MATLAB® code which may be included on thenon-transitory computer readable medium for the sake of this comparisonmay be seen in Example 2. Initially, a calibration may be performed,wherein a temperature pattern at the maximum load of the gas turbine iscalculated. Then, at separate time intervals, an array may be populatedwith data points for a plurality of temperature and pressure measurementdevices at the loads within the array, and corresponded to the givenload by taking the arithmetic average of the temperature and pressuremeasurements at given loads. This data may then be compared with datafrom similar gas turbine loads. After that, the collection oftemperature measurements across a given time may be averaged to producea pattern that is no longer a function of time, but a function ofazimuth or angle only. The pattern may then be subtracted from theaverage, and it may be doubled to simulate two paths around the gasturbine. The mean-subtracted temperature pattern may then be crosscorrelated against the temperature pattern of the gas turbine as maximumload, and the cross correlation parameter is then a shift correspondingto angular position. This may produce a correlation coefficient as afunction of angular shift, thereby indicating the magnitude of angularshift required for the mean-subtracted temperature field at maximumload. The angular shift with the maximum correlation coefficient may bethe relative swirl, indicating the amount of swirl at the current loadrelative to the swirl at maximum load.

According to certain embodiments, the non-transitory computer readablemedium may be included in a computer system comprising at least oneprocessor coupled to memory. In some embodiments, a gas turbine systemcomprising at least one gas turbine may provide data to the computersystem comprising the non-transitory computer readable medium. Thecomputer system may be configured to receive data input from at leastone thermocouple within the gas turbine, and the data input may beperformed in real time. The computer system may be configured to receivedata input from at least one pressure sensor, and the data input may beperformed in real time.

Also provided is a method for gas turbine maintenance, comprising:identifying a combustor in need of repair or replacement within a gasturbine; and repairing or replacing the combustor; wherein saididentifying comprises calculating base swirl of the gas turbine andcalculating relative swirl of the gas turbine in order to associate agas path from a thermocouple to the combustor in need of repair orreplacement.

According to certain embodiments, calculating base swirl comprisescalculating (a) unsteady pressure amplitude as a function of angularposition within the gas turbine and/or (b) mean-subtracted exhausttemperature as a function of angular position within the gas turbine.

Calculating unsteady pressure amplitude as a function of angularposition within the gas turbine and/or calculating mean-subtractedexhaust temperature as a function of angular position within the gasturbine may be done by azimuthal decomposition. Azimuthal decompositionis an acoustic and/or exhaust temperature approach wherein sine wavesare “fit” to a temperature pattern across angular position and/or anacoustics pattern across angular position. Any shift between the bestfit sine waves is the swirl as determined by azimuthal decomposition.Azimuthal decomposition calculates the cross-correlation between thecombustor unsteady pressure amplitude as a function of a predeterminedcan number within a combustor, which corresponds to a radial position,and the mean-subtracted exhaust temperature as a function of gas pathradial position. With this data, the radial offset between can numberand gas path number that maximizes a correlation coefficient isdetermined. This may be repeated for multiple data points as possible ina given power band. Next, for each power band, the method computes theaverage of the radial offsets that maximize the cross-correlationcoefficient. The result is an average radial offset between can number(which corresponds to an angular location) and gas path number (whichcorresponds to an angular location) as a function of load, this isdefined as the swirl. Azimuthal decomposition may be included in thecalculation of base swirl. The determination of base swirl may consistof azimuthal decomposition.

Calculating unsteady pressure amplitude as a function of angularposition within the gas turbine and/or calculating mean-subtractedexhaust temperature as a function of angular position within the gasturbine may be done by cross correlation. Cross correlation projects thecombustor pressure amplitude pattern onto the following expression:A*e{circumflex over ( )}(i*Θ_(d)), where A is a constant coefficient, iis the square root of −1, e is Euler's number, and Θ_(d) is the angularphase of the pressure amplitude pattern. Similarly, the mean-subtractedgas path temperature pattern is projected onto the function:B*e{circumflex over ( )}(i*Θ_(t)), where B is a constant coefficient, eand i are as defined above, and Θ_(t) is the angular phase of thetemperature pattern. This method then defines the swirl to be the phasedifference between the pressure amplitude pattern and the gas pathtemperature pattern. In degrees, this is equal to 2*π*(Θ_(t)−Θ_(d)). Theshift with the highest correlation to the observed temperature andpressure patterns represents the swirl. According to certainembodiments, this highest correlation to the observed temperature andpressure patterns may be represented as a single coefficient. Crosscorrelation may be included in the calculation of base swirl. Thedetermination of base swirl may consist of cross correlation.

The determination of base swirl may consist of azimuthal decompositionand cross correlation. Azimuthal decomposition and cross correlation mayboth be included in the calculation of base swirl, and may be providedas a check on one another. In certain embodiments, both azimuthaldecomposition and cross correlation are included in the determination ofbase swirl, and the determination of swirl in each is compared with oneanother to ensure a high confidence base swirl. The determination ofbase swirl may consist of azimuthal decomposition, cross correlation,and comparing the azimuthal decomposition swirl and cross correlationswirl.

Calculating relative swirl within a gas turbine may include autocorrelation. The relative swirl is the difference between the swirl atany given operating condition and the known swirl (reference swirl) at areference condition. The reference swirl may be known from experiencewith the gas turbine. The reference swirl may be determined by manuallycomparing pressure dynamics data to gas path temperature data. First,the auto correlation may average the mean-subtracted exhaust temperaturepattern for many samples at the reference condition, thereby definingthe reference pattern. Next, auto correlation may average themean-subtracted gas path temperature pattern over many samples at theoperating condition of interest, thereby defining the test sample. Thus,auto correlation correlates the reference pattern with the test pattern.Finally, auto correlation determines that the relative swirl is equal tothe correlation shift that gives the highest correlation coefficient.Auto correlation may be included in the determination of relative swirl.The determination of relative swirl may consist of auto correlation.

The disclosed method may provide that calculating base swirl comprisescalculating (a) unsteady pressure amplitude as a function of angularposition within the gas turbine and/or (b) mean-subtracted exhausttemperature as a function of angular position within the gas turbine. Insome embodiments, the method may provide that calculating base swirlcomprises calculating (a) unsteady pressure amplitude as a function ofangular position within the gas turbine and (b) mean-subtracted exhausttemperature as a function of angular position within the gas turbine.According to certain embodiments, calculating base swirl comprisesdetermining the average angular offset between the unsteady pressureamplitude as a function of angular position within the gas turbine andmean-subtracted exhaust temperature as a function of angular positionwithin the gas turbine. The average angular offset may be a function ofgas turbine load, or may be a function of gas turbine load only. In someembodiments, the average angular offset is independent of time.

The method of the disclosed embodiments may provide that calculatingbase swirl comprises: measuring pressure amplitude within the gasturbine; and fitting the pressure amplitude to the expressionA*e{circumflex over ( )}(i*Θ_(d)), wherein A is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(d) isthe angular phase of the measured pressure amplitude. In someembodiments, the fitting may be performed by taking a plurality ofpressure measurements, given by N, which may be equal to the number ofcombustors within the gas turbine. p_(n)(θ) may represent the N^(th)pressure amplitude as a function of angular position θ. From thesemeasurements, A and Â may be determined by the formulas:

$\hat{A} = {\frac{1}{N}{\sum\limits_{1}^{N}{{p_{N}(\theta)}e^{i\; \theta}}}}$A = Â θ_(d) = ∠ Â

According to certain embodiments, calculating base swirl comprises:measuring mean-subtracted gas path temperature within the gas turbine;and fitting the mean-subtracted gas path temperature to the expressionB*e{circumflex over ( )}(i*Θ_(t)), wherein B is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(t) isthe angular phase of the measured mean-subtracted gas path temperature.In some embodiments, the fitting may be performed by taking a pluralityof temperature measurements, given by M, which may be equal to thenumber of combustors within the gas turbine. T_(M)(θ) may represent theM^(th) exhaust temperature measurement as a function of angular positionθ. From these measurements, B and {circumflex over (B)} may bedetermined by the following formulas:

$\overset{\hat{}}{B} = {\frac{1}{N}{\sum\limits_{1}^{N}{{T_{M}(\theta)}e^{i\; \theta}}}}$$B = {\overset{\hat{}}{B}}$$\theta_{t} = {\angle \overset{\hat{}}{B}}$

In some embodiments, the method provides that calculating base swirlcomprises measuring pressure amplitude within the gas turbine andfitting the pressure amplitude to the expression A*e{circumflex over( )}(i*Θ_(d)), wherein A is a constant coefficient, i is the square rootof negative one, e is Euler's number, and Θ_(d) is the angular phase ofthe measured pressure amplitude. In certain embodiments, calculatingbase swirl comprises calculating a second swirl, wherein said secondswirl is 2*π*(Θ_(t)−Θ_(d)).

Calculating base swirl may comprise determining the average angularoffset between the unsteady pressure amplitude as a function of angularposition within the gas turbine and mean-subtracted exhaust temperatureas a function of angular position within the gas turbine, and whereinthe average angular offset is compared with the second swirl. An exampleof MATLAB® code which may be included on the non-transitory computerreadable medium for the sake of this comparison may be seen in Example1, which is provided only by way of example and not limitation.Initially, temperature and pressure amplitude patterns are determined atthe maximum load of the gas turbine. A variable may be assigned to themaximum load in megawatts, and as well as an array assigned to all ofthe data points at lower loads, wherein the load is measured as itsdifference from the maximum load. Then, data points are gathered for aplurality of temperature and pressure measurement devices at the loadswithin the array, and corresponded to the given load by taking thearithmetic average of the temperature and pressure measurements at givenloads. The difference between the temperature and pressure measurementsin terms of angular difference may be the swirl.

The method may further provide that a reference database is updated withbase swirl data as a function of gas turbine load. In some embodiments,a non-transitory computer readable medium may comprise instructions forupdating a reference database with base swirl data as a function of gasturbine load. According to certain embodiments, the reference databasemay be updated in real time. The reference database may be included onthe same non-transitory computer readable medium or on a separatenon-transitory computer readable medium. In some embodiments, the baseswirl may be calibrated only once from the reference database. Accordingto certain embodiments, the reference database is configured to beupdated with new data as directed by the user.

In certain embodiments, calculating relative swirl comprises calculatingthe difference between the base swirl and a reference swirl. The methodmay further provide that the reference swirl is retrieved from areference database, and wherein the reference swirl is selected on thebasis of turbine load. In some embodiments, the method may provide thatthe reference swirl comprises the mean-subtracted exhaust temperaturepattern for a plurality of samples.

According to certain embodiments, the relative swirl is equal to across-correlation shift, wherein the cross-correlation shift is a phaseshift that gives the highest correlation coefficient between the baseswirl and reference swirl. Initially, a calibration may be performed,wherein a temperature pattern at the maximum load of the gas turbine iscalculated. Then, at separate time intervals, an array may be populatedwith data points for a plurality of temperature and pressure measurementdevices at the loads within the array, and corresponded to the givenload by taking the arithmetic average of the temperature and pressuremeasurements at given loads. This data may then be compared with datafrom similar gas turbine loads. After that, the collection oftemperature measurements across a given time may be averaged to producea pattern that is no longer a function of time, but a function ofazimuth or angle only. The pattern may then be subtracted from theaverage, and it may be doubled to simulate two paths around the gasturbine. The mean-subtracted temperature pattern may then be crosscorrelated against the temperature pattern of the gas turbine as maximumload, and the cross correlation parameter is then a shift correspondingto angular position. This may produce a correlation coefficient as afunction of angular shift, thereby indicating the magnitude of angularshift required for the mean-subtracted temperature field at maximumload. The angular shift with the maximum correlation coefficient may bethe relative swirl, indicating the amount of swirl at the current loadrelative to the swirl at maximum load.

FIG. 1 is a block diagram illustrating certain embodiments of thepresent subject matter. The instructions 10 include calculating baseswirl 12 and calculating relative swirl 26. The calculation of baseswirl 12 includes azimuthal decomposition 14, cross correlation 16, orboth azimuthal decomposition 14 and cross correlation 16. Azimuthaldecomposition 14 outputs a swirl 18, and cross correlation outputs asecond swirl 20 independently. The swirl 18 and second swirl 20 may becompared 22 to ensure substantial agreement in the determination of baseswirl 12. The base swirl 12 provides an output of the swirl at base load24, which is passed to the determination of relative swirl 26. Utilizingthe swirl at base load 24 determined by the calculation of base swirl12, the determination of relative swirl 26 utilizes auto correlation 28to determine the relative swirl 26. The output of relative swirl 26 is adegree of swirl 30.

The following examples are set forth merely to further illustrate thesubject gas turbine swirl detection. The illustrative examples shouldnot be construed as limiting the subject matter in any manner.

EXAMPLE 1

Initially, temperature and pressure amplitude patterns are determined atthe maximum load of the gas turbine. A variable may be assigned to themaximum load in megawatts, and as well as an array assigned to all ofthe data points at lower loads, wherein the load is measured as itsdifference from the maximum load. Then, data points are gathered for aplurality of temperature and pressure measurement devices at the loadswithin the array, and corresponded to the given load by taking thearithmetic average of the temperature and pressure measurements at givenloads. The difference between the temperature and pressure measurementsin terms of angular difference may be the swirl, and in this particularexample, the reference swirl at maximum load. Averages can be subtractedfrom the arrays based on the computation of the arithmetic averages toobtain the mean-subtracted array. A mean-subtracted array can becross-correlated to obtain the reference swirl at maximum load.

%%%Comments are indicated in percentage symbols%%% %%%%% STEP 1- FindTemperature and Amplitude Patterns at max load %%%%%%%%% %% generatetemperature and amplitude patterns at max load loadTol = 10; %loadtolerance in MW maxLoadInds = find(abs(loads − maxLoad) <= loadTol);sampleT = TC_blocks_all(maxLoadInds,:); prime_ref_T =mean(sampleT,1)−mean(mean(sampleT)); sampleAmp =Amp_blocks_all(maxLoadInds,:); prime_ref_Amp = mean(sampleAmp,1)−mean(mean(sampleAmp)); %%%%% STEP 2- Cross-correlate %%%%%%%%% % Step 2may utilize a similar cross correlation strategy as shown in Example2%%%

EXAMPLE 2

Initially, a calibration may be performed, wherein a temperature patternat the maximum load of the gas turbine is calculated. Then, at separatetime intervals, an array may be populated with data points for aplurality of temperature and pressure measurement devices at the loadswithin the array, and corresponded to the given load by taking thearithmetic average of the temperature and pressure measurements at givenloads. This data may then be compared with data from similar gas turbineloads. After that, the collection of temperature measurements across agiven time may be averaged to produce a pattern that is no longer afunction of time, but a function of azimuth/angle only. The pattern maythen be subtracted from the average, and it may be doubled to simulatetwo paths around the gas turbine. The mean-subtracted temperaturepattern may then be cross correlated against the temperature pattern ofthe gas turbine as maximum load, and the cross correlation parameter isthen a shift corresponding to angular position. This may produce acorrelation coefficient as a function of angular shift, therebyindicating the magnitude of angular shift required for themean-subtracted temperature field at maximum load. The angular shiftwith the maximum correlation coefficient may be the relative swirl,indicating the amount of swirl at the current load relative to the swirlat maximum load.

%%%Comments are indicated in percentage symbols%%% %%%%%%%%%%%%%%%% STEP1- (CALIBRATION, may be done once) %%%%%%%%%%%%%%%% %% generatetemperature pattern at max load loadTol = 10; %load tolerance in MWmaxLoadInds = find(abs(loads − maxLoad) <= loadTol); sample =TC_blocks_all(maxLoadInds,:); prime_ref =mean(sample,1)−mean(mean(sample)); %%%%%%%%%%%%%%%% STEP 2- DO AT EACHTIME STEP %%%%%%%%%%%%%%%% %% At each time step, implement the following% find past times that have similar load to the present load loadInds =find(abs(loads−loads(t)) <= loadTol); % collect the temperaturemeasurements from all past times that had similar load (including thenewly added time step) sample = TC_blocks_all(loadInds,:); %Mean-subtract: Average the collection of temperature measurements acrosstime to produce a pattern that is only a function of azimuth/angle.Subtract from this pattern its average. prime_test =mean(sample,1)−mean(mean(sample)); % Take the vector of mean-subtractedtemperature pattern and repeat it once to double its length (as if youare going angularly around the engine two times) prime_long =[prime_test, prime_test]; % Cross correlate the mean-subtractedtemperature pattern against the temperature pattern belonging to maxload. The cross-correlation parameter (the shift parameter) is angularposition (azimuth). This will produce a correlation coefficient as afunction of angular shift (in other words, it will indicate how muchangular shift is required for the current mean- subtracted temperaturefield to look like the mean- subtracted temperature field at max loadshiftInds = [1:size(TC_blocks_all,2), 1:size(TC_blocks_all,2)]; rho =zeros(1,size(TC_blocks_all,2)); for shiftIndex = 1:size(TC_blocks_all,2)testSignal = prime_long(shiftIndex:shiftIndex+size(TC_blocks_all,2) −1);rhoMat = corrcoef(prime_ref,testSignal); rho(shiftIndex) = rhoMat(1,2);end % Find the angular shift that produced the maximum correlationcoefficient. This is the relative swirl (the amount of swirl at thecurrent load relative to the swirl at max load) rhoVec(t) = rho(rho ==max(rho)); shiftIndVec(t) = find(rho == max(rho));

It will be understood that the embodiments described herein are merelyexemplary, and that one skilled in the art may make variations andmodifications without departing from the spirit and scope of theinvention. All such variations and modifications are intended to beincluded within the scope of the invention as described and claimedherein. Further, all embodiments disclosed are not necessarily in thealternative, as various embodiments of the invention may be combined toprovide the desired result.

1. A non-transitory computer readable medium with instructions storedthereon, the instructions executable by one or more processors for:calculating base swirl in a gas turbine; and calculating relative swirlin the gas turbine.
 2. The non-transitory computer readable medium ofclaim 1, wherein calculating base swirl comprises calculating (a)unsteady pressure amplitude as a function of angular position within thegas turbine and/or (b) mean-subtracted exhaust temperature as a functionof angular position within the gas turbine.
 3. The non-transitorycomputer readable medium of claim 1, wherein calculating base swirlcomprises calculating (a) unsteady pressure amplitude as a function ofangular position within the gas turbine and (b) mean-subtracted exhausttemperature as a function of angular position within the gas turbine. 4.The non-transitory computer readable medium of claim 1, whereincalculating base swirl comprises determining the average angular offsetbetween the unsteady pressure amplitude as a function of angularposition within the gas turbine and mean-subtracted exhaust temperatureas a function of angular position within the gas turbine, wherein theaverage angular offset is a function of gas turbine load.
 5. Thenon-transitory computer readable medium of claim 1, wherein calculatingbase swirl comprises measuring pressure amplitude within the gas turbineand fitting the pressure amplitude to the expression A*e{circumflex over( )}(i*Θ_(d)), wherein A is a constant coefficient, i is the square rootof negative one, e is Euler's number, and Θ_(d) is the angular phase ofthe measured pressure amplitude.
 6. The non-transitory computer readablemedium of claim 1, wherein calculating base swirl comprises measuringmean-subtracted gas path temperature within the gas turbine and fittingthe mean-subtracted gas path temperature to the expressionB*e{circumflex over ( )}(i*Θ_(t)), wherein B is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(t) isthe angular phase of the measured mean-subtracted gas path temperature.7. The non-transitory computer readable medium of claim 6, whereincalculating base swirl comprises measuring pressure amplitude within thegas turbine and fitting the pressure amplitude to the expressionA*e{circumflex over ( )}(i*Θ_(d)), wherein A is a constant coefficient,i is the square root of negative one, e is Euler's number, and Θ_(d) isthe angular phase of the measured pressure amplitude, whereincalculating base swirl comprises calculating a second swirl, whereinsaid second swirl is 2*π*(Θ_(t)−Θ_(d)).
 8. The non-transitory computerreadable medium of claim 7, wherein calculating base swirl comprisesdetermining the average angular offset between the unsteady pressureamplitude as a function of angular position within the gas turbine andmean-subtracted exhaust temperature as a function of angular positionwithin the gas turbine, and wherein the average angular offset is crosscorrelated with the second swirl.
 9. The non-transitory computerreadable medium of claim 1, wherein a reference database is updated inreal time with base swirl data as a function of gas turbine load. 10.The non-transitory computer readable medium of claim 1, whereincalculating relative swirl comprises calculating the difference betweenthe base swirl and a reference swirl.
 11. The non-transitory computerreadable medium of claim 10, wherein the reference swirl is retrievedfrom a reference database, and wherein the reference swirl is selectedon the basis of turbine load, wherein the reference swirl comprises themean-subtracted exhaust temperature pattern for a plurality of samples.12. The non-transitory computer readable medium of claim 10, wherein therelative swirl is equal to a cross-correlation shift, wherein thecross-correlation shift is a phase shift that gives the highestcorrelation coefficient between the base swirl and reference swirl. 13.A gas turbine system comprising: a computer system comprising at leastone processor coupled to memory and the computer readable medium ofclaim 1; and at least one gas turbine, wherein the computer system isconfigured to receive real time data input from at least onethermocouple, wherein the computer system is configured to receive realtime data input from at least one pressure sensor.
 14. A method for gasturbine maintenance, comprising: identifying a combustor in need ofrepair or replacement within a gas turbine; and repairing or replacingthe combustor; wherein said identifying comprises calculating base swirlof the gas turbine and calculating relative swirl of the gas turbine inorder to associate a gas path from a thermocouple to the combustor inneed of repair or replacement.
 15. The method of claim 14, whereincalculating base swirl comprises calculating (a) unsteady pressureamplitude as a function of angular position within the gas turbineand/or (b) mean-subtracted exhaust temperature as a function of angularposition within the gas turbine.
 16. The method of claim 14, whereincalculating base swirl comprises calculating (a) unsteady pressureamplitude as a function of angular position within the gas turbine and(b) mean-subtracted exhaust temperature as a function of angularposition within the gas turbine.
 17. The method of claim 14, whereincalculating base swirl comprises determining the average angular offsetbetween the unsteady pressure amplitude as a function of angularposition within the gas turbine and mean-subtracted exhaust temperatureas a function of angular position within the gas turbine, wherein theaverage angular offset is a function of gas turbine load.
 18. The methodof claim 14, wherein calculating base swirl comprises measuring pressureamplitude within the gas turbine and fitting the pressure amplitude tothe expression A*e{circumflex over ( )}(i*Θ_(d)), wherein A is aconstant coefficient, i is the square root of negative one, e is Euler'snumber, and Θ_(d) is the angular phase of the measured pressureamplitude.
 19. The method of claim 14, wherein calculating base swirlcomprises measuring mean-subtracted gas path temperature within the gasturbine and fitting the mean-subtracted gas path temperature to theexpression B*e{circumflex over ( )}(i*Θ_(t)), wherein B is a constantcoefficient, i is the square root of negative one, e is Euler's number,and Θ_(t) is the angular phase of the measured mean-subtracted gas pathtemperature.
 20. The method of claim 19, wherein calculating base swirlcomprises measuring pressure amplitude within the gas turbine andfitting the pressure amplitude to the expression A*e{circumflex over( )}(i*Θ_(d)), wherein A is a constant coefficient, i is the square rootof negative one, e is Euler's number, and Θ_(d) is the angular phase ofthe measured pressure amplitude, wherein calculating base swirlcomprises calculating a second swirl, wherein said second swirl is2*π*(Θ_(t)−Θ_(d)).
 21. The method of claim 20, wherein calculating baseswirl comprises determining the average angular offset between theunsteady pressure amplitude as a function of angular position within thegas turbine and mean-subtracted exhaust temperature as a function ofangular position within the gas turbine, and wherein the average angularoffset is cross correlated with the second swirl.
 22. The method ofclaim 14, wherein a reference database is updated in real time with baseswirl data as a function of gas turbine load, wherein calculatingrelative swirl comprises calculating the difference between the baseswirl and a reference swirl, wherein the reference swirl is retrievedfrom a reference database, and wherein the reference swirl is selectedon the basis of turbine load, wherein the reference swirl comprises themean-subtracted exhaust temperature pattern for a plurality of samples,wherein the relative swirl is equal to a cross-correlation shift,wherein the cross-correlation shift is a phase shift that gives thehighest correlation coefficient between the base swirl and referenceswirl.